1. Field of the Invention
The present invention relates generally to positive displacement devices, for example devices using pistons in cylinders such as pumps, compressors, expanders and internal and external combustion engines, and more particularly, to positive displacement devices using purely rotary movement.
2. Description of the Prior Art
A wide variety of positive-displacement pumps are known in the art for pumping liquids and compressing gases. For example, a number of positive-displacement pumps are shown and described by Wilson, "Positive-Displacement Pumps", Product Engineering, Jun. 6, 1960, pages 42-51. Many such pumps develop rotary motion to displace the liquid being pumped, but such "rotary" motion is often eccentric, orbital, or accompanied by linear reciprocal motion. Such motions limit the speed and efficiency at which such positive-displacement pumps can be operated. Excessive speeds result in unacceptable vibration and rapid wear.
U.S. Pat. No. 1,599,778 issued to Loftus discloses a metering pump for pumping fluids and includes a rotor having an even number of radial slots extending from the center of the rotor and terminating near the rim thereof. A series of rollers are secured to a rotatable disk, the rollers being designed to fit closely within the radial slots of the rotor. The disk carrying the rollers is offset from the center of the rotor, and the centers of the rollers pass through the center of the rotor. The fluid to be pumped is drawn into the device from an inlet chamber in communication with peripheral ports formed near the rim of the rotor at each radial slot. Fluid is discharged from the pump either by a pipe connected to the center of the rotor or by an outlet chamber in communication with the peripheral port at the end of each rotor adjacent the rim thereof.
The metering pump disclosed in the '778 Loftus patent uses pure rotary motion. However, by admitting the fluid to be pumped into the peripheral ends of the radial slots formed in the rotor, the pump disclosed by Loftus is not efficient at high speed operation. Centrifugal force developed by the rotating motion of the device acts against fluid attempting to enter the peripheral end of the radial slot. Clearly, the aforementioned centrifugal force developed by the rotation of the rotor opposes the partial vacuum created by the pistons as they move away from the peripheral end of the radial slots while passing by the inlet chamber.
Additionally, in the apparatus disclosed by the '778 Loftus patent, the rolling motion of the roller disk can engage only one side of the radial slot at any moment in time, thus leaving a gap for the leakage of fluids on the side of the roller disk not contacting the wall of the radial slot. If there were a true "sliding seal" formed between the roller and both side walls of the radial slot, then the claimed roller motion could not actually be achieved. Thus, the amount of pressure or compression which can be obtained from such a structure is significantly limited.
Furthermore, the pump disclosed by the '778 Loftus patent does not include any mechanism for synchronizing the rotation of the rotor and the roller disk; instead, the rolling force of the rollers bearing against the walls of the radial slots causes the rotor to advance. Over time, the constant pressure exerted by the rollers against the side walls of the radial slots causes wear which continually increases leakage between the side walls of the pistons and the mating side walls of the radial slots.
In addition, the rollers disclosed by the '778 Loftus patent are cylindrical in cross-sectional shape and develop only a line contact between the periphery of the roller and the side walls of the radial slot. Accordingly, and at best, only a sliding line seal is maintained between the rollers and the walls of the radial slot, as compared with the conjugate surface seal of a conventional piston and cylinder commonly used in reciprocating piston pumps and compressors. The line contact developed by the cylindrical rollers disclosed by Loftus limits the vacuum which can be developed by such a pump and is not as effective in maintaining a fluid-tight seal between the roller and the side walls of the radial slot as is a device which has working elements having conjugate surfaces that wipingly engage each other.
Apart from rotary motion pumps, rotary motion internal combustion engines are also well known. For example, the Wankle rotary internal combustion engine is known to those in the art of engine design and has been somewhat successful in the marketplace. U.S. Pat. No. 1,166,999, issued to Loftus, discloses an explosive engine having a structure similar to that disclosed in the aforementioned '778 Loftus patent. A series of rollers are supported for rotation by a pinion, and the rollers mesh with elongated radial slots formed in a rotating rim eccentric to the pinion. A spark plus is fitted within an ignition port to ignite explosive gases compressed by a roller that had advanced within a radial slot. However, this device suffers from the same disadvantages as described above in regard to the '778 Loftus patent.
Accordingly, it is an object of the present invention to provide a pure rotary positive displacement device which will function in any application which utilizes a piston and a cooperating cylinder and which will pump, compress, or expand a fluid as described above, but wherein the admission of the fluid to be pumped, compressed or expanded is admitted to one or more of such cylinders at a point other than its peripheral end to avoid the necessity of overcoming centrifugal force in order to fill each cylinder with such fluid.
It is another object of the present invention to provide such a pure rotary positive displacement device wherein the rotational movement of the rotor or cylinder housing, and the piston or pistons, are synchronized for maintaining the movement of the pistons along the center lines of the cylinders to minimize friction therebetween and to minimize wear of such components.
It is still another object of the present invention to provide such a pure rotary positive displacement device which utilizes one or more pistons which may be other than cylindrical in shape and which increase the area of the sliding seal contact between the side walls of the pistons and the mating side walls of the cylinders to minimize leakage and achieve greater compression.
It is yet another object of the present invention to provide such a pure rotary positive displacement device which may be constructed as a highly compact device and which may be operated at relatively high speeds to provide a sizeable flow rate.
These and other objects of the present invention will become more apparent to those skilled in the art as the description thereof proceeds.
Because the shapes of the working elements in this invention are unusual with respect to what is common in the art, it is necessary that clear definitions be established. A cylinder is a passageway for a piston, but in this invention, such cylinders are not necessarily circular in cross section, but may also be rectangular, elliptical or any other useful shape. A cylinder extends radially outward from the center of its housing, and always has a corresponding opposing cylinder on the same centerline at 180 degrees thereto. Thus the cylinders are always even in number, with a minimum of two. When only two cylinders are used, the two radial cylinders effectively merge with each other to form a single cylinder which extends diametrically through the cylinder housing. Preferably, a piston has, in cross section, the same shape as the cylinder in which it moves. The number of pistons is usually one half the number of cylinders. In this invention, rotating pistons and cylinders are analogous to conventional reciprocating pistons and cylinders in function.